The analysis of data from Justice's Executive Office of U.S. Attorneys also found:

In the eight months ending in May, Justice attorneys declined to prosecute more than nine out of every 10 terrorism cases sent to them by the FBI, Immigration and Customs Enforcement and other federal agencies. Nearly 4 in 10 of the rejected cases were scrapped because prosecutors found weak or insufficient evidence, no evidence of criminal intent or no evident federal crime.

Since the Sept. 11, 2001, attacks, only 14 people have been sentenced to 20 years or more in prison in terrorism cases. Of the 1,329 convicted defendants, only 625 received any prison sentence. More than half got no prison time or no more than they had already served awaiting their verdict.

The report comes at a difficult time for the Bush administration: It is sagging in public-opinion polls just before congressional midterm elections. Democrats hope to regain control of at least one house of Congress, and President Bush has urged Republicans to run in part on his record in the war on terrorism.

"There are many flaws in the report," said Justice Department spokesman Bryan Sierra. "It is irresponsible to attempt to measure success in the war on terror without the necessary details about the government's strategy and tactics."

For instance, Sierra said, prison sentences are "not the proper measure of the success of the department's overall counterterrorism efforts. The primary goal ... is to detect, disrupt and deter terrorist activities."

TRAC totaled the cases that prosecutors labeled as terrorism or anti-terrorism no matter what charge was brought. It found only 14 prosecutions in fiscal 2000. That rose to 57 in fiscal 2001, which ended three weeks after the 9/11 attacks. The figure then soared to 355 in fiscal 2002. But by fiscal 2005, it dropped to 46. And in the first eight months of fiscal 2006, through May, there were only 19 such prosecutions.

Past critics of administration tactics found both favorable and unfavorable possible explanations. The sharp decline in prosecutions might show that prosecutors have moved away from "all kinds of secondary infractions" they pursued early on, said Steven Aftergood, director of the Federation of American Scientists' government secrecy project. Those early cases drew criticism that Arab Americans were rounded up based on mere racial profiling.

The small number of long prison sentences shouldn't be a surprise because "terrorism is actually very rare -- far more people are killed in ordinary street crime," said James Dempsey, policy director of the Center for Democracy and Technology.

Nevertheless, terrorism poses a risk of catastrophic loss of life, "so agencies must pursue a lot of leads that do not pan out," Dempsey added. "We can't blame the FBI for pursuing those leads, but we can blame them and the Justice Department for arresting people and making a big media splash when things don't pan out."

Meredith Fuchs, general counsel at the National Security Archive at George Washington University, said the light sentences could mean "we are catching people at the margins, not at the center of the plots."

"The surge right after 9/11 make sense," Fuchs added, "but the drop-off so quickly means either a lot of that post-9/11 activity was not necessary or that they haven't identified key people or that key people in custody aren't being prosecuted."

Although prosecutors suggested they might be charged somewhere someday, the government has never disproved persistent allegations they were tortured during interrogations overseas and thus cannot be tried in U.S. courts.

If prosecutions "have been compromised by unlawful interrogation or surveillance, that would be worse than ironic," Aftergood said. "It would mean the government has performed in a self-defeating manner."

Justice reported in June that 441 defendants were charged and 261 convicted or pleaded guilty in terrorism or terrorism-related cases from investigations conducted primarily after Sept. 11. Citing those figures, Sierra said the department's strategy "has helped protect this country from terrorists since the attacks of September 11th."

Unlike the data from the Executive Office of U.S. Attorneys, the June figures did not contain definitions of which cases were looked at. Former New York Times reporter David Burnham, TRAC's co-director, said Justice officials declined to give TRAC the definitions used in compiling the June figures on grounds that might undermine anti-terrorism enforcement.